This invention relates generally to apparatus associated with electrographic process stations, and more particularly to apparatus for establishing a predetermined interface between a discrete dielectric sheet and an electrographic process station.
In U.S. Pat. No. 4,436,405 issued Mar. 13, 1984, in the name of Kindt, an electrographic copier is described which utilizes a plurality of discrete photoconductive sheets. The sheets are transported seriatim about a continuous path into operative relation with electrographic process stations to make information reproductions. In the reproduction process carried out at such process stations of the copier, a sheet is uniformly charged and then exposed by an image of information (e.g. a document) to be reproduced to form a latent image charge pattern on such sheet corresponding image-wise to such information. The charge pattern is developed with pigmented thermoplastic electroscopic marking particles electrostatically attracted to the charge pattern to form a visible transferable image. The transferable image is then transferred from the sheet to a receiver member to form the information reproduction, and the sheet is cleaned for reuse. An advantage of using the plurality of discrete photoconductive sheets, as contrasted to the use of a continuous photoconductive web or drum, is that the speed of the sheets, as they move through the process stations, can be varied to optimize the operation of each process station on the sheets.
The discrete photoconductive sheets must be accurately positioned relative to the respective electrographic process stations while in operative relation to such stations. That is, every sheet must exhibit the same predetermined interface with a particular process station over their respective surface areas. For example, in the charging station, the point-to-point spacing from the corona charger to the surface of a sheet as the sheet travels past the charger must be equal to ensure that a uniform charge is laid down on the sheet; and in the transfer station, successive elements of the sheet surface must be uniformly associated with a receiver member to ensure complete transfer of a marking particle image on the sheet to the receiver member.
In the aforementioned Kindt patent, an arrangement is provided for transferring images from discrete photoconductive sheets to receiver members, and a track assembly supporting opposed marginal edges of sheets guides such sheets through other of the electrographic stations. Such transfer arrangement requires that the sheets be stopped during transfer. Stoppage of the sheets, while having certain advantages, complicates the construction of the transfer apparatus arrangement and may increase the overall process time required to make a reproduction. Further, the track assembly for guiding the sheets relies on the beam strength of the sheets to support such sheets over their respective surface areas to ensure uniformity of process station function on the sheets at the interface of the sheets to the process stations. Such beam strength may not always be sufficient to ensure the desired interface to accomplish such uniformity of function.